A significant trend throughout integrated circuit (IC) development is the downsizing of IC components. As the size reduces, the performance requirements become more stringent. Also, as devices continue to shrink in size, the channel region continues to shrink as well. For metal-oxide-semiconductor field effect transistors (MOSFETs), increased performance requirements have generally been met by aggressively scaling the length of the channel region. However, such a short channel length faces high electric field and manufacturing limits.
Epitaxial SiGe regions or other epitaxial source/drain regions improve transistor performance by increasing the mobility of the carriers in the channel region of the PMOS or NMOS transistors which result from the intentionally created lattice mismatch that induces mechanical stress or strain across the channel region. For example, a compressively-strained channel provides an improved hole mobility that is beneficial for PMOS transistors by increasing the PMOS drive current. However, during the epitaxial growth, the etchant gases or corrosive gases easily penetrate into the substrate, thus altering a profile of the source/drain region.